On thermohaline structure and circulation of the Western Large Aral Sea from 2009 to 2011: Observations and modeling

Abstract

The shrinkage of the Aral Sea in the second half of the past century has significantly affected the hydrophysical regime of the lake. The objective of this paper is to report on a hydrological structure and circulation of the today's Aral Sea based on both direct field observations and modeling results. We focus on the results of three field surveys to the Aral Sea which took place in the period from 2009 to 2011. In addition, series of numerical experiments using Princeton Ocean Model adapted to the Aral Sea was undertaken to investigate the contributions from bathymetry and water stratification in the formation of the basin scale circulation. The hydrological structure of the Aral's western basin in autumn season exhibited a three-layered pattern with two local salinity maxima, separated by a fresher intermediate layer. According to direct observations, water circulation in the surface layer has anti-cyclonic character, while circulation in the bottom layer has cyclonic sign under the predominant northerly winds. The simulation experiments demonstrated clearly that the main cause of the anti-cyclonic circulation in the surface layer of the lake is the "asymmetric" bathymetry with broad shallow area along the eastern coast and relatively steep and deep western slope. However, strong stratification is a necessary condition for the formation of the cyclonic circulation gyre in the bottom layer.

The internal seiche field in the changing South Aral Sea (2006–2013)

“…The stratification was weak in 2006 and strong in 2013, but this is merely circumstantial; it depends solely on the time when the campaigns were carried out. In general, this hypersaline lake becomes saltier but the maximum annual density gradient decreases (Izhitskiy et al, 2014a). The elongated horizontal dots on the 2013 profile (Fig.…”

“…The ongoing changes in the Aral Sea are being closely followed by the scientific community (Singh et al, 2012;Schettler et al, 2013;Shi et al, 2014). Since 2002, the evolution of its stratification has been documented (Zavialov, 2005Izhitskiy et al, 2014a, b), the predominant circulation has been described (Izhitskiy et al, 2014a) and the role played by geomorphological processes associated with hydrodynamics in the evolution of the lake has been discussed (Roget et al, 2009). However, due to a lack of data, only very preliminary works exist on internal waves.…”

“…In 2013, during a field campaign that was not focused on the study of internal waves, continuous temperature data within the water column were recorded for the first time, making it possible to use the Princeton Ocean Model (POM) to assess the numerical results for the internal seiches. The POM, which is widely known, has been used to make marine forecasts for the US Great Lakes (NOAA-GLERL, 2016), to study internal waves (Rueda et al, 2003;Munroe and Lamb, 2005;Babu and Rao, 2011) and to study the Aral Sea (Roget et al, 2009;Izhitskiy et al, 2014a).…”

Present state of the Aral Sea: diverging physical and biological characteristics of the residual basins

“…Field observations were conducted in collaboration with a number of institutions in Russia and Central Asia’s states of Uzbekistan and Kazakhstan. The previous fifteen surveys of the program between 2002 and 2013 were mainly limited to the Large Aral Sea 10 11 12 , and did not include the Small Aral Sea or Lake Tshchebas. In view of the ongoing profound changes of the Aral ecosystem, we expanded the area of observations ( Fig.…”

The Aral Sea as Natural Solar Pond: Extremal Thermal and Mixing Conditions

“…Кроме того, в значительной степени менялись гидрофизические и гидрохимические характеристики вод моря. Так, например, западный бассейн Большого Арала стал гипергалинным водоемом с высокой плотностной стратификацией вод [2,3].…”